The data transfer rate over a wireless communication network is recently increasing rapidly. This results from the appearance and spread of a variety of devices, such as smart phones and tablet PCs which require Machine-to-Machine (M2M) communication and a high data transfer rate. In order to meet a necessary high data transfer rate, carrier aggregation technology in which more frequency bands are efficiently used, cognitive radio, and multiple antenna technology and multiple base station cooperation technology in order to increase a data capacity in a limited frequency, etc. are recently emerging.
Furthermore, a wireless communication network is evolving into an increase in the density of accessible nodes around a user. Here, the nodes mean antennas or a group of antennas that are spaced apart from one another at specific intervals in a Distributed Antenna System (DAS). However, the nodes are not limited to the meaning, but may be used as a broader sense. That is, the node may be a pico-cell eNodeB (PeNB), a home eNodeB (HeNB), a Remote Radio Head (RRH), a Remote Radio Unit (RRU), a relay or the like. A wireless communication system including such nodes having a high density may show better system performance through cooperation between the nodes. That is, if each of the nodes operates as an independent base station (i.e., a Base Station (BS), an Advanced BS (ABS), a Node-B (NB), an eNode-B (eNB), or an Access Point (AP)), the transmission and reception of each node are managed by one control station, and thus the nodes operates like antennas or a group of antennas for one cell, the nodes may show much excellent system performance as compared with a case where the nodes do not cooperate with each other. A wireless communication system including a plurality of nodes is hereinafter called a multi-node system.
In general, a node may be applied to a group of antennas spaced apart from one another at specific intervals or higher and also to a specific antenna group irrespective of the interval although it is defined as the specific antenna group. For example, a BS formed of cross-polarized antennas may be considered to include a node formed of an H-pol antenna and a node formed of a V-pol antenna.
In a multi-node system, a node for sending a signal to a terminal (or user equipment (UE)) may be different every terminal, and a plurality of nodes may be configured. Here, each node may send a different reference signal. In such a case, the terminal can measure a channel state for a relation between each node and the terminal using a plurality of reference signals and can feed back channel state information periodically or aperiodically.